Ultrasonic wave device



1967 R. 1'. DENTON ETAL 3,397,32Q

ULTRASONIC WAVE DEVICE Filed Sept. 26, 1962 VTTR/UM ALUM/A/UM GAR/V5(NO/V- MAGNET/C) VTTR/UM mo/v l6 GARNET (MA G/VE TIC) FIG. 2

VTTR/UM IRON VTT/P/UM ALUM/NUM CARA/5 T VO/V-MAG/VET/C) JUNCTION W/ THCON Tl/VUOUS CRYSTAL LATTICE 1 r DEA/TON ZS E. a. SPENCER A T TORNE VUnited States Patent Office 3,307,120 ULTRASONHC WAVE DEVICE Richard T.Denton, South Plainfield, and Edward G.

Spencer, Berkeley Heights, N.J., assignors to Bel! TelephoneLaboratories, Incorporated, New York, N.Y., a corporation of New YorkFiled Sept. 26, 1962, Ser. No. 226,381 Claims. (Cl. 333-30) Thisinvention relates to ultrasonic delay line devices and more particularlyto the construction of efficient magnetic transducers for these delaylines.

Recently it has been recognized that small elements of certainmagnetically polarized materials of the types which exhibit gyromagneticeffects may be employed as generators for ultrasonic vibrations atmicrowave frequencies. The element is biased by a direct-currentmagnetic field and the microwave frequency magnetic field is introducedperpendicular to the biasing field. By what presently appears to be acomplicated mixture of gyromagnetic precession and magnetostriction, anultrasonic wave will be produced in the material which will betransferred into a connected delay medium. Analysis of certain aspectsof the involved phenomenon may be found in articles by C. Kittel in 110Physical Review 836, May 15, 1958; Brommel and Dransfeld in 3 PhysicalReview Letters 83, July 15, 1959; Schlomann in 31 Journal of AppliedPhysics 1647, September 1960; and Spencer, Denton and Chambers in 125Physical Review 1950, March 15, 1962.

It has been proposed that the gyromagnetic element, which preferablytakes the form of a thin disc, be bonded to a delay medium constructedby conventional delay line material. These bonds can be made to transmitultrasonic energy efficiently at low frequencies but at frequenciesroughly above 100 megacycles per second these bonds introduce largeinsertion losses between the transducers and the delay medium with aconsequent inefficiency. Alternatively, it has been proposed to form thedelay line itself as well as the transducer from the same member ofgyromagnetic material. A biasing field and a radio frequency field areapplied so that an end surface or end film of the member constitutes thetransducer. While such a homogeneous construction eliminates the bond,it has been found that the biasing field incidently magnetizes theentire member of magnetic material and becomes a relatively inefiicientpropagation medium for the ultrasonic waves due to its gyromagneticlosses. It has been further recognized that the polarized nature of themagnetized propagation medium has undesirable efiects upon propagationthrough it in any direction other than one parallel to the applied fielddirection.

It is therefore an object of the present invention to increase theefficiency and flexibility of ultrasonic delay line devices employingmagnetic transducers.

In accordance with the present invention, the delay line is composed ofa nonmagnetic material having a crystal structure and unit cell sizesimilar to that of the magnetic transducer material, with the transducermaterial grown epitaxially upon the delay line material. Thus, the delayline together with its transducer constitutes a single extendedcrystalline lattice, a portion of which is magnetic and the remainder ofwhich is nonmagnetic. Specific examples to be described include magneticyttrium iron garnet grown upon a delay line of nonmagnetic yttriumaluminum garnet or yttrium of gallium garnet, or magnetic magnesium ironoxide grown upon magnesium aluminate.

A feature of the invention resides in the particular coupling circuitemployed to support and apply the radio frequency magnetic field to themagnetic transducer portion.

3,3h7,l2 Patented Feb. 28, 1967 These and other objects, the nature ofthe present invention, its various features and advantages will appearmore fully upon consideration of the various illustrative embodimentsnow to be described in detail in connection with the accompanyingdrawings, in which:

FIG. 1 is a perspective view, partly in cross-section of a delay lineinterconnected between a pair of transducers in accordance with theinvention; and

FIG. 2 illustrates the application of the invention to a multiplereflection form of relay device.

Referring more particularly to FIG. 1, an illustrative embodiment of theinvention is shown comprising a delay line in the form of a cylindricalrod 12 formed from a single crystal of nonmagnetic material andtransducer layers 13 and 14 formed upon each of its ends as acontinuation of the same crystal lattice from a nonconduc tive, magneticmaterial of the type having substantial gyro magnetic properties. Thenature of both the magnetic and nonmagnetic materials will be describedin more detail hereinafter. The dimensions and crystalline orientationof rod 12 are selected to produce the desired ultrasonic delay and modeof propagation at the frequency of interest. Radio frequency energy atmicrowave frequencies is coupled into and out of layers 13 and 14 by anovel coaxial coupling. Thus, an input coaxial line 15 located adjacentto layer 13 with the outer conductor electrically and mechanicallyconnected to conductive ring 16 which surrounds the end of rod 12 andlayer 13. The center conductor 17 of coax 15 passes across the face oflayer 13 and electrically terminates on the opposite side of ring 16.Ring 16 serves the dual function of providing a rigid support for coax15 and rod 12 and also serves as the ground plane for the radiofrequency fields supported between conductor 17 and ring 16 by means ofwhich a circularly polarized component of radio frequency magnetic fieldis excited in the plane of layer 13. A direct-current biasing field isapplied by means not illustrated in detail in a direction normal to theplane of layers 13 and 14. This field is represented schematically bythe vector H and has a strength that biases the gyro-margnetic materialof layers 13 and 14 into the neighborhood of ferromagnetic resonance. Asa result of a mixture of the gyrornagnetic precession about the biasingfield and magnetostriction as described in the abovementionedpublications, circularly polarized acoustical waves are excited in layer13 and are transferred to rod 12 through which they travel to the outputtransducer comprising layer 14, conductor 18 and ring 19 by which theenergy is reconverted into a microwave signal upon coax 21).

A principal feature of the present invention resides in the nature ofthe material comprising the transducer layers 13 and 14, the material ofrod 12 and the juncture therebetween. The material of each layer ispreferably one of the known nonconducting magnetic materials whichexhibits gyromagnetic properties at microwave frequencies and which, inaddition, has reasonably low magnetic losses, large magnetoe-lasticcoupling constant, high acoustical Q and may be grown in single crystalform. One of the most suitable materials for this purpose is yttriumiron garnet. Having thus selectedthe gyromagnetic material which is toconstitute the transducer, the material to form rod 12 is thenparticularly chosen in accordance with the principles of the presentinvention. Thus, the material for rod 12 is one that has a similarity in'both crystalline structure and unit cell size to that of thegyromagnetic material so that the gyromagnetic material may beepitaxially grown upon the cylindrical end of the rod as a continuationof the crystal lattice thereof. In particular, when yttrium iron garnetis employed as the gyromagnetic material, a single crystal ofnonmagnetic yttrium aluminum garnet is preferred for rod 12. Othercombin 3 ations of magnetic and nonmagnetic materials will be set forthhereinafter.

Several methods for epitaxially depositing materials of the types hereconsidered are familiar to the art and it appears necessary only tosummarize one particularly suitable method for the purpose of thepresent disclosure. In general, the process is similar to the seededflux growths heretofore employed to grow single crystal magneticmaterials. The primary diiference resides in the fact that for thepresent process the seed comprises the substrate member of nonmagneticmaterial constituting the delay media. Typically, the process includesthe steps of combining the reactants of the magnetic material to begrown in the proper proportions with a flux comprising lead oxide, leadborate, lead fluoride, boron oxide or combinations thereof, heating themixture to form a homogeneous solution of the reactants, inserting theseed crystal, and cooling the mixture very slowly to room temperature.Further details of these processes may be found in Patents 2,957,827 and3,050,407 granted to J. W. Nielsen, October 25, 1960, and August 21,1962; or in the copending application of J. P. Remeika, Serial No. 28,-862, filed May 13, 1960.

In particular, to grow layer 13 of yttrium iron garnet epitaxially uponrod 12 of yttrium aluminum garnet, the reactants yttrium oxide and ironoxide are weighed, mixed together and placed in a suitable cruciblealong with a flux such as lead oxide. The crucible is heated to fuse thellux and reactants and to form a homogeneous melt. A temperature ofapproximately 1200" F, appears satisfactory. T he end of rod 12, whichhas been squared and polished, is lowered into the melt and thetemperature is reduced. Thereupon yttrium iron garnet will begin to formupon the yttrium aluminum garnet rod as a continuation of the crystallattice of the substrate. Cooling is continued until the growth issufficient to produce a layer thickness that is on the order of at leastone-half a wavelength of the intended ultrasonic frequency. Typically,this occurs after a temperature reduction of several hundred degrees.The rod 12 is then removed, cooled to room temperature whereupon thelayer is shaped and polished to the precise thickness desired.

The preceding discussion has been directed specifically to thecombination of yttrium iron garnet and yttrium aluminum garnet as thetransducer and delay line materials, respectively. These materials areamong the familiar and useful magnetic and nonmagnetic compounds havingthe garnet structure. Like aluminum, however, gallium and other GroupIII elements may be substituted for the iron in the basic'garnetstructure to produce a nonmagnetic material. Note, however, thataluminum and gallium produce crystals of unit cell size most similar toiron and are, therefore, most readily epitaxially grown upon each otherby present techniques.

Another structural class of magnetic and nonmagnetic materials that maybe used to practice the present invention comprise those of spinelcrystalline structure' Of this class, magnesium iron oxide haspronounced gyromagnetic properties and has been successfully grown upona substrate of magnesium aluminate. This class appears to beparticularly attractive from an economical standpoint because of theWell known lower cost of the material and processing for the spinels ascompared to the .garnets. It is also possible by processes well knownfor the spinels to produce a gradual single crystal transition fromnonmagnetic to magnetic composition.

Other magnetic and nonmagnetic constituents may, of course, be added asis the practice in the art to improve the properties of either themagnetic or nonmagnetic por tions. In the case of the garnet class thisincludes materials formed from rare earth elements other than yytrium.Therefore, the present invention contemplates a member having a singlecrystalline lattice structure, a portion of which is magnetic andincludes a magnetic constituent such as iron and the remainder of whichis 4- nonmagnetic and includes instead nonmagnetic constituents such asaluminum.

The term epitaxial as used herein should be understood in its broadestsense as designating a process by which one material is grown ordeposited upon a base material that is somewhat different, either interms of composition, impurity content, or other property, and in whichthe grown material is deposited in a crystal structure, the orientationof which is determined by the crystal orientation of the base materialto form with a base a continuous crystal lattice. It includes, inaddition to the flux growth process described above, those processesreferred to in the art as hydrothermal synthesis, flame fusion andequivalent processes. In addition, a diffusion process may be employedby which sufiicient quantities of magnetic material are added into thecrystal structure of the nonmagnetic base to produce a magnetic layertherein.

The present invention represents an improvement over either a magnetictransducer bonded to conventional nonmagnetic delay line or ahomogeneous magnetic structure in which both transducer and delay lineare formed from the same magnetic crystal. As to the first, theepitaxiaily formed junction according to the present invention providesa rigid, unitary connection without the mechanical problems of the bond.Further, since the interface between the transducer material and thedelay line material is a continuation of the same crystal lattice,ultrasonic energy can be efficiently transferred across it even atmicrowave frequencies. As to the second prior art form, the difiicultyand expense of growing single crystals of magnetic material are reducedby the use of more easily grown nonmagnetic materials as the delay line.Moreover, a magnetic delay medium, particularly in the presence of theresidual biasing field which extends into it from the transducer and maybias it in the vicinity of gyromagnetic resonance, has substantiallygreater acoustical propagation losses than nonmagnetic materials.

The principles of the present invention are particularly advantageouswhen applied to any of the various iorms of polygonal or multifacetdelay lines in which the ultrasonic wave is multiply reflected from aplurality of faces. The reason for this advantage will be apparent fromFIG. 2 which shows a polygonal body 39 in one of the preferred forms asdescribed in Patent 2,839,731 granted June 17, 1958, to H. I. McSkimin.Ultrasonic wave energy launched within body 30 is multiply reflected asrepresented by path 39 until it returns to the output transducer.

In accordance with the present invention, body 30 is formed from acrystal of nonmagnetic material of the type described above and isshaped according to the teachings of the above-mentioned McSkiminpatent. A1 ternative shapes may be found in the teachings of D. L.Arenberg, 20 Journal of Acoustical Society 1, 1948. The input and outputtransducers comprise layers 31 and 32 of gyromagnetic material which areepitaxially formed upon the selected faces of body 30. The radiofrequency input and output are illustrated schematically by coaxialconductors 35 and 36 ending in loops 37 and 38, respectively, with theplane of the loops oriented normal to the facesof the respective layers31 and 32. Steady biasing fields represented by vectors 33 and 34 areapplied respectively to layers 31 and 32 in a direction normal to theplane of each layer.

It will be readily apparent that if body 30 were forme of magneticmaterials, -as in the case of the homogeneous magnetic construction ofthe prior art, the presence of steady biasing fields 33 and 34 of thetransducers would extend also into body 36, magnetically polarizing body30 along the axes of the fields and thereby destroying its cubicsymmetry. The multiply reflected ultrasonic waves which necessarilycross these polarized axes at random angles will be greatly distortedand dispersed due to the preference of the ultrasonic wave to propagateparallel to the polarized axes. However, since body 30 is nonmagneticwhen constructed according to the invention, its symmetrical nature isunaffected by magnetic fields.

In all cases it is to be understood that the abovedescribed arrangementsare merely illustrative of a small number of the many possibleapplications of the principles of the invention. Numerous and variedother arrangements in accordance with these principles may readily bedevised by those skilled in the art without departing from the spiritand scope of the invention.

What is claimed is:

1. An ultrasonic delay device comprising a member having a transducerportion formed of magnetic material and a delay line portion formed ofnonmagnetic material, means including means for applying a radiofrequency magnetic field to said magnetic portion for generatingultrasonic wave energy and means for utilizing ultrasonic wave energyconnected to said nonmagnetic portion, said magnetic and nonmagneticmaterials both being single crystal materials of given crystal latticestructure,

the junction between said portions being formed as a continuous crystallattice structure extending from and including the crystal lattice ofsaid magnetic portion to and including the crystal lattice structure ofsaid nonmagnetic portion so that no acoustical discontinuity ispresented to said wave energy traversing said junction.

2. An ultrasonic device according to claim 1 wherein said magneticmaterial is yttrium iron garnet and wherein said nonmagnetic material isyttrium aluminum garnet.

3. An ultrasonic device according to claim 1 wherein said magneticmaterial is magnesium iron oxide and wherein said nonmagnetic materialis magnesium aluminate.

4. An ultrasonic device of the type in which a transducer including anelement of magnetic materials suitably excited to generate ultrasonicwave energy is mechanically coupled to a delay line for conveying saidgenerated elastic wave energy away from said transducer characterized inthat the material of said delay line is nonmangetic and has a crystalshape that is the same as the crystal shape of said magnetic materialand a crystal lattice structure and unit cell size that are similar tothe crystal lattice structure and unit cell size of said magneticmaterial.

5. An ultrasonic device according to claim 4 wherein said magneticmaterial and said nonmagnetic material both form a single continuouscrystal lattice.

6. An ultrasonic device according to claim 4 wherein said magneticmaterial is a compound including iron in a given crystalline structureand wherein said nonmagnetic material is a compound including an elementfrom Group III in said given crystalline structure.

7. An ultrasonic device comprising a member of nonmagnetic materialhaving a crystal structure and unit cell size for receiving andtransmitting ultrasonic wave energy,

a layer of magnetic material having a crystal structure and unit cellsize similar to that of said member formed epitaxially upon a surface ofsaid member, means for applying a steady magnetic field to said layerand means for applying a high frequency radio magnetic field to saidlayer in a direction normal to said steady field for converting saidhigh frequency field into an ultarsonic wave for transmission into saidnonmagnetic member.

8. An ultrasonic device according to claim 7 wherein said means forapplying said high frequency field comprises a ring of conductivematerial surrounding said layer and a two-conductor transmission linefor said energy having one conductor thereof connected to said ring onone side of said layer, the other conductor thereof extending acrosssaid layer and being connected to said ring on the other side of saidlayer.

9. An ultrasonic device according to claim 7 wherein said nonmagneticmember comprses yttrium aluminum garnet and wherein said magnetic layercomprises yttrium iron garnet formed as a continuation of the crystalstructure of said nonmagnetic member.

10. An ultrasonic delay device comprising a member having at least anend portion which is of magnetic material of the type which exhibitsgyromagnetic properties at high frequencies, means utilizing saidgyromagnetic properties for generatng ultrasonic wave energy at saidhigh frequencies comprising a ring of conductive material surroundingsaid end portion, a two conductor transmission line for high frequencyradio energy having one conductor thereof connected to said ring on oneside of said portion, the other conductor thereof extending across saidportion and being connected to said ring on the other side of saidportion, means for applying high frequency radio energy between saidconductors, and means for applying a steady magnetic field to saidportion in a direction normal to said other conductor, and means forconveying said generated elastic wave energy away from said portion.

References Cited by the Examiner UNITED STATES PATENTS 2,571,019 10/1951Donley 33330 2,712,638 7/1955 Arenberg 333-30 2,718,637 9/1955 Goodwin343-7.7 3,037,174 5/1962 Bommel 333-30 3,098,204 7/1963 Brauer 33330OTHER REFERENCES Bommel and Dransfeld, Phys. Rev. Letters, July 15,1959. Pages 8384.

Le Craw, Phys. Rev. Letters, vol. 8, pages 397-99, May 1962.

HERMAN KARL SAALBACH, Primary Examiner. C. BARAFF, Assistant Examiner.

1. AN ULTRASONIC DELAY DEVICE COMPRISING A MEMBER HAVING A TRANSDUCERPORTION FORMED OF MAGNETIC MATERIAL AND A DELAY LINE PORTION FORMED OFNONMAGNETIC MATERIAL, MEANS INCLUDING MEANS FOR APPLYING A RADIOFREQUENCY MAGNETIC FIELD TO SAID MAGNETIC PORTION FOR GENERATINGULTRASONIC WAVE ENERGY AND MEANS FOR UTILIZING ULTRASONIC WAVE ENERGYCONNECTED TO SAID NONMAGNETIC PORTION, SAID MAGNETIC AND NONMAGNETICMATERIALS BOTH BEING SINGLE CRYSTAL MATERIALS OF GIVEN CRYSTAL LATTICESTRUCTURE, THE JUNCTION BETWEEN SAID PORTIONS BEING FORMED AS ACONTINUOUS CRYSTAL LATTICE STRUCTURE EXTENDING FROM AND INCLUDING THECRYSTAL LATTICE OF SAID MAGNETIC PORTION TO AND INCLUDING THE CRYSTALLATTICE STRUCTURE OF SAID NONMAGNETIC PORTION SO THAT NO ACOUSTICALDISCONTINUITY IS PRESENTED TO SAID WAVE ENERGY TRAVERSING SAID JUNCTION.